J. Buongiorno / Spring 2005
22.313J, 2.59J, 10.536J THERMAL-HYDRAULICS IN POWER TECHNOLOGY
Homework Set 3
Steam Separation in a PWR U-tube Steam Generators
The schematic of a PWR U-tube Steam Generator (SG) is shown in Figure 1. Saturated steam at
5.7 MPa and 11% quality is generated in the U-tube bundle region. The majority of the liquid is
removed in the steam separator. The residual liquid is removed in the steam dryer. The steam
flow rate to the turbine is 456 kg/s. The properties of steam and water at 5.7 MPa are reported in
Table 1.
Steam to
Turbine
Steam
Dryer
Steam
Separator
Riser
Feedwater
Primary
Water In
Primary
Water Out
Figure 1. U-tube Steam Generator
Steam Separator
You are to consider a steam separator design based on gravity separation.
i)
ii)
iii)
Calculate the minimum height of the region above the free liquid surface that
minimizes carryover. (Hint: the riser has a flow area of 7.07 m2, and is partitioned, so
that its equivalent diameter is 0.2 m)
Calculate the separation efficiency of the gravity separator. (Hint: ignore the effect of
steam carryunder)
Estimate the maximum diameter of the entrained droplets. (Hint: use a value of 22 for
the critical Weber number)
J. Buongiorno / Spring 2005
iv)
Gravity separators are not actually used in PWR steam generators.
separators are used instead. Why?
Cyclone
Steam Dryer
Now consider a steam dryer design of the chevron type. The height of the chevrons is 1 m, the
spacing is 15 mm, wave amplitude is 12.5 mm, the wavelength is 50 mm and the length is 100
mm (= 2 wavelengths).
v)
vi)
vii)
Calculate the minimum number of chevrons required to obtain a 20% margin to liquid
re-entrainment in the dryer. (Hint: use Figure 2 to calculate the breakthrough velocity
for the dryer)
Calculate the separation efficiency of the dryer, assuming a flat distribution for the
diameter of the entrained droplets.
Repeat ‘vi’ for chevrons of same height, spacing and wave amplitude, but 86 mm
wavelength and 172 mm length (= 2 wavelengths). Which design would you choose?
Table 1. Properties of saturated water at 5.7 MPa.
Parameter
ρf
ρg
hf
hg
Cp,f
Cp,g
μf
μg
kf
kg
σ
Value
764 kg/m3
29 kg/m3
1,196 kJ/kg
2,788 kJ/kg
5.2 kJ/(kg°C)
4.7 kJ/(kg°C)
1.0×10-4 Pa⋅s
1.8×10-5 Pa⋅s
0.59 W/(m°C)
0.06 W/(m°C)
0.021 N/m
Figure 2. Breakthrough velocity in chevron separators.